Interleaved Practice Benefits Learning and Transfer

When you sit down to practice a skill, the intuitive approach is to drill one thing until it sticks, then move to the next. This is blocked practice. The alternative, interleaving, mixes different problem types or tasks together so you rarely do the same thing twice in a row. Decades of work show that the intuitive choice is usually the wrong one.

Worse during practice, better on the test

The defining feature of interleaving is that it feels harder and looks worse while you do it. Schorn and Knowlton (2021) had participants practice three different motor sequences in a serial reaction time task, either blocked or interleaved. Blocked practice produced faster responses during training. But when participants returned the next day, the interleaved group retained more and, critically, transferred better to entirely novel sequences. Those who had trained in blocked fashion were thrown off when the test mixed sequences together; their learning was less flexible and more fragile to a change in conditions. The interleaved group performed well regardless of how the test was arranged.

What makes their result striking is that it held even for participants who reported no awareness of the underlying sequences. The benefit of interleaving reaches implicit, procedural learning, not just the deliberate, conscious kind.

A desirable difficulty

This pattern is the signature of a desirable difficulty: a manipulation that depresses performance during acquisition while strengthening long-term retention and transfer. The same dissociation appears across domains. Rohrer and Taylor (2007) found that college students who practiced mixed mathematics problems performed worse during practice but vastly outperformed the blocked group on a delayed test a week later. Kornell and Bjork (2008) showed that interleaving paintings by different artists, rather than studying each artist’s work in a block, produced better ability to identify the painter of new, unseen works, even though most learners believed blocking had helped them more.

Why it works: forcing discrimination

The leading mechanism is that interleaving forces the learner to discriminate. When problems of one type are blocked together, you can apply the same procedure on autopilot without ever deciding which procedure the problem calls for. Mixing types restores that decision. Each trial requires retrieving not just how to execute a solution but which solution applies, and that act of discrimination is exactly what a real test, or real life, demands. This is why interleaving is especially powerful for inductive category learning and for any task where the hard part is telling similar cases apart.

Why it matters for sequencing practice

For tutoring and ed-tech, the lesson is direct and slightly uncomfortable. A practice set that keeps a learner succeeding lesson by lesson may be optimizing for the wrong signal. Smooth, confident practice predicts poor retention; effortful, mixed practice predicts durable skill. Systems that sequence problems should resist the pull toward neat blocks, mix problem types across a session, and treat a dip in immediate accuracy as a feature rather than a bug.